The present invention relates to a method for manufacturing a color filter and more particularly to a method that can easily form a lens with a small radius of curvature.
In recent years, solid state image sensing devices which are able to replace an electron tubes and thus are spotlighted as the image sensing device of the next generation can achieve the color by forming the color filter at the upper side of optical-to-electrical converting region.
In such a prior art solid state image sensing devices, MOS transistors, photo transistors, and CCD's (Charge Coupled Devices) are widely used.
In case of CCD's which is mainly used in a small-sized movie cameras, a large number of pixels and high sensitivity are demanded and thus a technology to form the lens for condensing the light on the color filter is developing.
Similarly, LCD's (Liquid Crystal Displays) achieve the colorful image by forming the color filter on the optical-to-electrical converting region.
There are divided into two kinds according to the components. One is an organic filter which are made by dyeing organic matters such as casein and gelatin and the other is an inorganic filter which utilizes the optical interference phenomenon. In particle, the organic filter is more widely used than the inorganic one since the organic filter is a moderate prices rather than the inorganic one.
FIG. 1(A)-(C) are series of cross sectional views of processes for manufacturing a conventional color filter for a CCD.
In FIG. 1(A), there is a CCD where a silicon substrate 1 has a concave and convex surface and photodiodes 2, 3, and 4 are formed in a matrix shape on the concave portions of surface, while conducting and insulating layers 5 and 7 are formed on the convex portions of surface.
A flatting layer 9 is formed on the surface of the CCD by using a transparent material such as polyimide and on this flatting layer 9, a dyed layer 11, which is made of casein comprising (NH.sub.4) .sub.2 Cr.sub.2 O.sub.1 or gelatin comprising (NH.sub.4).sub.2 Cr.sub.2 O.sub.1 and is colored with dyestuffs, is formed corresponding to the photodiode 2.
At this time, the layer 11 is dyed with one of the materials such as magenta, cyan, and yellow. Subsequently, an interlayer 13 is formed by deposition of polyimide.
Referring to FIG. 1(B), the dyed layers 15, 19 and an interlayers 17, 21 are sequentially formed on the interlayer 13 in the same manner as described above. The interlayers 17 and 21 is used to prevent the mixing of colors of the dyed layers 15 and 19.
Next, a layer for a lens, which is made of acrylate material, is formed on the entire surface of the interlayer 21 and then lens patterns 23 are formed by exposure and development process with a desired distance l.sub.1.
As shown in FIG. 1(C), by annealing the lens patterns 23, lenses 25, 26, and 27 which corresponds respectively to the photodiodes 2, 3, and 4 are formed. The annealing is sequentially carried out from low to high temperature.
By this thermal processing, the edge portions of the lens patterns 23 are molten and subsequently the top sides of the lens patterns 23 are bulged like a spherical surface by surface tension and gravity, while the bottom sides are extended, thereby forming the lenses 25, 26, and 27 apart from each other with a desired distance l.sub.2.
As a materials forming lenses affect the effect of gravity rather than the surface tension by the thermal, when the lenses are formed by the thermal processing, it is difficult to obtain thick lenses with a small radius of curvature.
Also, the lens materials to be formed by the thermal treatment are extended during the thermal processing, so that the distance between the lenses is difficult to control precisely.